1. Field of the Invention
This invention relates to digital-signal-processing apparatus and method as well as a program product therefor.
2. Description of Related Art
In the digital signal processing, a signal with a desired band width has been passed through a finite-duration impulse response (FIR) filter or an infinite-duration impulse response (IIR) filter. If processing the digital signal using the FIR filter, so-called Gibbs phenomenon in the Fourier transform occurs because an infinite impulse response of ideal filter is finitely carried out, thereby resulting in an occurrence of ringing in transition regions from a passing region to blocking region and vice versa.
In order to reduce such any adverse effect of the ringing, so-called window function to multiply a transition in the signal by a small coefficient has been used to suppress the ringing. Further, a first low-pass filter having a sharp blocking property and a second low-pass filter having a loose blocking property are provided and a mixture ratio of the digital signals output from the first and second low-pass filters alters near a position where a signal level alters like a step, thereby suppressing the ringing (see Japanese Patent Application Publication No. H08-79558).